1. Field of the Invention
The present invention provides a method for measuring different characteristics of a magneto-resistive head for a hard disk drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. There have been developed magnetic heads that have a write element for magnetizing the disks and a separate read element for sensing the magnetic fields of the disks. The read element is typically constructed from a magneto-resistive material. The magneto-resistive material has a resistance that varies with the magnetic fields of the disk. Heads with magneto-resistive read elements are commonly referred to as magneto-resistive (MR) heads.
FIG. 1 shows an MR head 1 which has an abut junction design. This type of MR head has a pair of permanent magnets 2 located on either side of a sensor element 3. The permanent magnets provide a hard bias field that stabilize the sensor element 3.
Magnetic heads are typically tested before being assembled into disk drives. Errors in the manufacturing processes may create instabilities in the biasing junction. The stability of the heads are typically tested to screen for defective parts. Stability factors such as amplitude covarian and base line popping noise are tested by loading a head onto a test stand and performing test routines. The test routines include the steps of writing a signal on a track and then reading the signal with the magneto-resistive read element of the head. The signal is typically read when the read element is aligned with the center of the track. Such a procedure does not test for junction effects and is generally not effective in determining an instability of the head.
One embodiment of the present invention is a method for measuring a characteristic of a magnetic head of a hard disk drive. The method includes the step of writing a signal onto a track of a disk. The track has left and right track edges. The magnetic head is moved to align junction areas of the head with the track edges. The characteristic is then measured. These steps may be repeated to align various junction areas with track edges and to measure various characteristics of the head.